A battery is an electrochemical element, with an internal resistance that increases greatly as soon as its capacity is nearly exhausted. This exhaustion can be caused by normal discharge when current is supplied to a current consuming component as well as by self-discharge during non-use or storage, or by a combination of these effects.
Most electronic instruments, and, in particular, electronic watches, have two power consumption states which may be recurrent or not, corresponding to the states defined as minimum current and high current. Generally, the instrument fails when making the transition to high current operation. It is at such times that, if the internal resistance of the battery has increased, the drop in voltage is sufficient to disrupt the operation of the current consuming component.
In, for example, an analog watch, the high current state is recurrent. At each second, the current drawn by the motor, added to that continuously drawn by the electronic circuit, causes a drop in the voltage which may disrupt the operation of the motor or the electronic circuit. It is thus wise to continually detect the dicharge state of the electric battery. Prior to the present invention, there was no reliable procedure or apparatus for determining with certainty the state of an electric battery of a precision instrument which was adaptable to conform to a variety of externally selectable parameters.